Steam Oxidation Behavior of Austenitic Heat Resistant Steel NF709 at 700 ℃

The oxidation kinetics, the morphology and distribution of chemical composition of oxidaion layers for NF709 austenite heat-resisting steel in water vapor at 700 ℃ were studied by the oxidation weight gain method, SEM with EDS and XRD. The results indicate that the oxidation kinetics of this steel under water-vapor condition follows parabolic equation Δm=ktz at 700 ℃. The thickness of oxidation layer increased with test time. The oxidation scale consists of two layers, the outer layer rich in Fe oxide with a loose and porous structure is more thicker than the inner layer rich in Cr oxide with dense spinel structure. The element diffusion was retarded by the inner layer and so the oxidation rate decreased.